Biocontrol method in aquaculture for rearing the swimming crab larvae Portunus trituberculatus

The aim of this work is to control the waterenvironment for culturing larvae of the swimmingcrab, Portunus trituberculatus, using microorganisms.The bacterial strain PM-4 (Thalassobacter utilis)improved the survival rate of crab larvae andrepressed the growth of Vibrio anguillarum (bacterium)and Haliphthoros sp.(fungus) in seawater. PM-4 wascultured and added daily to seawater during the firstto third zoean growth stage of the crab with diatomsand rotifers. Numbers of PM-4 decreased in culturewater during the first 3 days, because of feeding bythe first zoean stage of larvae. The finalconcentration of PM-4 was 105 to 106 cellsml−1according to the plate count method in larval rearingwater.During 1989 to 1993, we tried seed productions of aswimming crab in 200 m3 containers at TamanoStation, Japan Sea-Farming Association. In 33trials of the biocontrol methods, average survivalrate of crab larvae was 28.3% when the bacterialstrain PM-4 was added. In 42 trials in which the strainPM-4 was not added, average survival rate of crab larvae was15.6%. We conclude that thebacterial strain PM-4 is effective as a biocontrolagent.